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' G; S. MAYHEW. COMPOSITION BLAOKBOARD.

No. 535,916. Patented Mar. 19, 1895.

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G. S. MAYHEW. comrosmou BLAUKBOARD.

No. 535,916. Patented Mar. 19, 1895.

aren't FFICEQ GEORGE S. MAYHEWV, OF MINNEAPOLIS, MINNESOTA, ASSIGNOR TO CHARLES A. SMITH, OF SAME PLACE.

COMPOSITION BLACKBOARD.

SPECIFICATION forming part of Letters Patent No. 535,916, dated March 19, 1895. Application filed July 20, 1894- serial No. 518,083. (No model.)

To all whom it may concern.-

Be it known that I, GEORGE S. MAYHEW, of the city of Minneapolis, county of Hennepin, State of Minnesota, have invented certain new and useful Improvements in Oomposition Blackboards, of which the following is a specification.

My invention relates to a composition blackboard for use in school rooms, shops and other places where large boards are required, as

well as for smaller tablets, slates, due.

The object of my invention is to provide an artificial board having a hard stone-like surface which when prepared with a black com- I 5 position and given a smooth surface will fulfill all the purposes of black-boards;

A further object is to provide a stone finished artificial board which will be non-resonant, light and durable and which will not shrink nor swell or bulge; and a further object is to provide a composition board which may be worked with ordinary wood working tools.

To this end my invention consists in a comz 5 position material having a hard surface, which hard surface may adapt the board for either ornamental or useful purposes, all as hereinafter described and particularly pointed out in the claims.

The invention will be more readily understood by reference to the accompanying drawings, in which-- Figure 1 is a perspective view showing a black-board embodying myinvention as it appears in use. Fig. 2 is an enlarged sectional view thereof. Fig. 3 is an enlarged detail perspective view of a section of the board or material. Fig. 4 illustrates the manner of preparing the insets which receive the plas- 0 tic material of which the hard surface is composed.

As shown in the drawings, the base of my board or material is composed .of a series of narrow, thin and long wooden slats 2, placed edge to edge and between heavy sheets 3and 4 of straw or wood pulp paper, all of these parts being firmly cemented together by a suitable adhesive compound. This base after being dried is passed through a sand papering machine to even and smooth the outer surface 5 thereof, or, if desired both sides of the board, the sand paper removing the slight irregularities and bunches upon the surface of the thick paper which might otherwise show through the finish. After this operation 5 5 a thinner sheet 6 of very soft porous paper is glued andpressed upon the smooth surface of the base. The material is then dried and next passed between spur rolls similar to that shown in Fig. 4. The spurs are staggered upon the roll and as the board is passed under the roll at a different speed from the speed of the roll the spurs are forced into the top of the board, passing through the thin soft sheet, through the thick paper sheets and 6 5 into the wooden parts, making dove tailed recesses or insets 10, therein. These insets are closely arranged across the whole surface of the board, the spaces between the same being an inch more or less in size. A thick coat- 7o ing of adhesive material is then applied to the bottom or back of the board or base, and the thick paper sheet 7 is applied thereto. This paper sheet is provided with a Water proof surface 8 and after being waterproofed and before 7 being applied to the board is thoroughly saturated with moisture.

The outside layer 9 is composed of composition material which when dry has a hard stony character, While adapted to take the place of natural stone or slate. This layer is blown, rolled or otherwise applied to the surface of the board, and while in a plastic state thereon portions of it enter the insets 10 in the surface of the board and take the form of small dove-tailed tenons 11 which dry with the other part and eifectually prevent the flaking off or cracking of parts of the hard coat or layer.

For black-board purposes a black artificial compound is used, but for other uses other hard drying compounds or compositions may be employed.

The wet sheet 7 having the water proof outer surface or skin is made of substantially 5 the same thickness as the thickness of the hard coat or layer plus the thickness of the thin soft sheet, and its office is to counteract the warping effect which would otherwise result from the drying of the hard layer. As roo arranged it is obvious that the hard compound will dry slowly from the outside inwardly, and the thick sheet 7 on the opposite side of the board will dry in substantially the same manner and the same time, owing to the fact that the water proof skin thereof prevents the more rapid evaporation of the moisture. The thin soft sheet which is interposed between the hard layer and the base of the board serves two purposes, a minor one being the absorption of surplus moisture on the plastic compound when first applied to prevent the moisture passing through into the base to loosen the cement therein, and the more important office being to deaden the sound of blows or strokes upon the hard surface, the sound being effectually intercepted and taken up by the soft material. The employment of the small tenons is particularly important, as this material is made up in boards which are often eighteen to twenty feet long and from four to six feet wide. When these boards are lifted up by the ends the hard surface is apt to crack slightly, and while such cracks will not show when the board is put in place the hard material would be apt to flake off if it were not for the closely arranged tenons which hold each part of it firmly in place.

A boardof the construction described is extremely light and durable and will not shrink or warp or swell or bulge, so that it is particularly adapted for black-board use. Furthermore these boards may be used upon walls without intervening frame Work to hold them in shape; and further the waterproof back of the board effectually avoids any detrimental action of the mosture from wet walls.

The thickness of the board may be varied at will depending only upon the use to which it is to be put, and as the hard case is comparatively thin it does not prevent the Working of the material with ordinary carpenters tools.

Having thus described my invention, I claim as new and desire to secure by Letters Patent 1. The combination,inacomposition board, of a suitable base having thick paper facings or sides, with a sheet of soft paper secured upon one side of said base, a layer of originally plasticbut hard drying compound applied to said sheet of soft paper, and a thick sheet of paper applied to the other side of said base, said sheet being of the thickness of said layer of hard drying compound plus the thickness of said sheet of soft paper, and said thick sheet having a water-proof outer surface or skin, substantially as described.

2. The combination, in a composition material, of the base made up of strips of wood and thick sheets of paper inclosing the same, said parts being firmly cemented together, with a thin sheet of soft paper applied to one side of said base, said side of the base being provided with numerous perforations or insets extending through both sheets and into the wood, a layer or coating of hard drying stony compound applied upon said sheet of soft paper, parts of the compound being pressed into said insets to form retaining tenons, and a thick water-proof surfaced paper sheet applied to the opposite side of the base, substantially as and for the purpose specified.

3. The process of manufacturing composition material, which consists in first providing a suitable and comparatively thin base, and then applying a coating of a hard drying stony composition to one side thereof, then thoroughly saturating a sheet of paper or pulp board having a water proof outer surface and as thick as said coating, then applying said saturated sheet to the opposite side of said base, and finally drying the whole, substantially as described.

In testimony whereof I have hereunto set my hand this 7th day of July, A. D. 1894.

' GEORGE S. MAYHEVV.

In presence of C. G. HAWLEY, M. E. GooLEY. 

